A significant number of people are undergoing intensive insulin therapy to manage their diabetes, whereby they determine their blood glucose level at each meal (e.g., breakfast, lunch, dinner, snack time) for use with other factors to assess the insulin dose needed. Intensive insulin therapy usually involves injections of regular-acting or rapid-acting insulin before each meal (i.e., bolus dose), as well as one or more injections of intermediate-acting or long-acting insulin every day (i.e., basal dose) or the use of an insulin pump to provide both the basal and bolus doses. By adjusting the amount of insulin to match blood sugar levels and the amount eaten at each meal, the goal of intensive insulin therapy is to keep blood sugar levels at or near normal throughout the day.
People on intensive insulin therapy use guidelines provided by their doctor to base the amount of insulin that they will need on what they are planning to eat, how much activity they plan to do, and what their current blood glucose level is. With this kind of planning, they have a lot of flexibility in what they can eat, when they can eat, and how active they can be. As discussed in more detail below, intensive insulin therapy requires diabetes education, careful planning, and strong commitment to be safe and successful. Patients must learn how food, exercise, and insulin affect their blood sugar, and adjust their insulin to keep their blood sugar levels within a target range.
The amount of carbohydrates in a patient's diet directly affects the amount and type of insulin that the patient needs in an intensive insulin regimen. When carbohydrates are processed by the digestive system, they are converted into sugar (glucose) and used by the body's cells as energy. Insulin helps to get the glucose into the cells, and the amount of insulin that is needed to do this varies with the amount of carbohydrates that were eaten by the patient. Normally, the pancreas handles the insulin production process. If a patient practices intensive insulin therapy, the patient mimics the effect of the pancreas by counting the amount of carbohydrates he plans to eat and then figuring out how much insulin he will need to manage them (i.e., food dose). The balance of these two amounts is called the patient's carbohydrate-to-insulin ratio. For example, if a patient's personal CIR is one unit of insulin for every 15 grams of carbohydrates, and the total carbohydrate grams in the food he plans to eat is 45 g, he will need three units of insulin to cover the meal. A dietitian or other health care provider generally must explain how to calculate the CIR ratio, which is different for each person, varies with the time of day, may change over time and is difficult to estimate. In addition to knowing planned carbohydrate intake and CIR, a patient needs to factor in how far off their current blood glucose level is from a target level at the beginning of a given meal-time period and take extra insulin if the glucose is high or less insulin if the glucose is low (i.e., correction dose).
Patients will often make corrections to their insulin doses based upon how far their actual premeal blood glucose value is from their premeal target glucose value (i.e., a correction dose). The correction dose is determined by the insulin sensitivity factor, ISF, which is the amount that 1 unit of insulin will lower the blood glucose value, as described in more detail below. The dose is the difference of the current blood glucose value from the target glucose value, divided by the ISF. It may be positive and therefore imply that the patient will take extra insulin, or negative and therefore imply that the patient will reduce their dose of insulin.
Many patients on intensive insulin therapy calculate each insulin dose. The total dose is the food dose plus the correction dose. They count carbohydrates and utilize the carbohydrate-to-insulin ratios (CIRs) when they eat so they can calculate their food dose. In addition, they will make necessary correction to their insulin doses by calculating a correction dose. They take insulin at the proper time before meals (if scheduled) and monitoring their blood sugar level at least four times a day to know what corrections need to be made to their insulin dose. The patient must use a CIR developed for him by his healthcare professionals so that he can use the amount of carbohydrates he plans to eat to determine how much insulin he needs to inject for food. Thus, this method also requires counting carbohydrates. They also must use an ISF developed for him by a healthcare professional so that he can use the variation of current blood glucose from the target value to determine how much insulin he needs to correct for a currently abnormal blood glucose value.
As stated above, home diabetes therapy requires a patient to carry out a prescribed regimen that involves self-testing blood glucose levels and administering appropriate doses of insulin. Glucose levels are monitored at periodic intervals to determine when another insulin injection should be taken or to determine how the user is responding to prior injections. The patient monitors blood levels by lancing a portion of the body with a lancet, for example, to take a blood sample or by using a subcutaneous glucose monitoring device, among other methods. A blood sample drawn, for example, via a lancet is then placed on a test strip that contains appropriate reagents for creating the chemical reactions necessary to measure glucose levels, which is subsequently analyzed by a blood glucose monitor. The patient then manually records the results, the time and date in a log book or in the blood glucose monitor. Alternatively, the blood glucose monitor automatically determines blood glucose levels (e.g., via a subcutaneous sensor) and stores the results and corresponding dates and times in a computerized memory device. The patient then determines the amount of medication (e.g., insulin) needed based on tested blood glucose levels and planned food intake and uses a medication delivery device (e.g., a syringe, medication delivery pen or infusion pump) to deliver the appropriate amount of insulin. The afore-mentioned and commonly assigned U.S. patent application Ser. No. 10/153,883, filed May 24, 2002, discloses a diagnostic and medication delivery system for monitoring blood glucose levels and recording insulin intake, for example. A diagnostic and medication delivery system is also described in commonly assigned U.S. Pat. No. 6,192,891, which is also expressly incorporated herein in its entirety.
Most patients undergoing insulin therapy for managing their diabetes have difficulty determining how much insulin they need. As described above, the dose needed is dependent on how many carbohydrates were ingested over a particular period (e.g., periods extending from breakfast to lunch, lunch to dinner, dinner to snack before bedtime, or periods extending over other mealtimes or snack times), and how far their blood glucose levels are off from a therapeutic target level. In addition to the patients' carbohydrate to insulin ratio (CIR), another important factor for insulin dose determination is insulin sensitivity factor (ISF) or correction factor (CF). The ISF is understood to be the expected drop of glucose concentration when 1 Unit (U) of insulin is administered to a patient. The ISF is individual to the patient and is determined over a period of time. A common ISF is 30-50 mg/dL per unit of insulin. A starting CIR often used is 5-15 grams of carbohydrate per unit of insulin. Both constants (CIR and ISF) may be different for each meal and are adjusted based on current data from blood glucose values, insulin doses and meal sizes. These adjustments are very complex, and few patients understand how to do them. Many healthcare professional also find adjusting these constants to be a daunting process.
Thus, medical nutrition therapy is a critical component of therapy for patients on insulin. While meal portion sizes and estimates of carbohydrate servings (15 grams) and carbohydrate counting are concepts that can be learned, accurate insulin dose determination is too difficult for some patients, even if they are provided with the CIR and ISF. Few patients are capable of accurately determining the CIR and ISF themselves. A patient who finds self-determination of his CIR too difficult may opt to have his CIR determined for him by a healthcare provider. Such a determination of CIR by a healthcare provider also has drawbacks. First, the patient must supply the provider with extensive data relating to blood sugar levels, times of blood glucose testing, results and insulin doses, among other information such as stress level, exercise, and so on, which can be time consuming and inconvenient. Second, a patient may not have any access or sufficiently frequent access to a provider for the provider to be able to make adequate adjustments to the patient's diabetes management formula and/or its various factors (e.g., CIR, ISF and so on). Finally, many providers have difficulty determining these constants from all of the data and tend to guess at the value based upon only one or two data points.
A need therefore exists for a simplified method for patients on insulin therapy and for their healthcare providers to determine their carbohydrate to insulin ratio (CIR) and their insulin sensitivity factor (ISF) from available blood glucose, food and insulin data.